1. Field of the Invention
The present invention is directed to methods and signals for ultra wideband communications, and more particularly to methods and signals for conveying application data via carrierless ultra wideband wireless signals.
2. Discussion of the Background
Digital information typically takes the form of a stream of binary pulses of a square wave, each pulse representing a bit (i.e., 1 or 0) of data. To transmit a digital stream of data, it is well known to use the digital data stream to modulate a carrier waveform and to transmit the modulated carrier waveform rather than the digital waveform. By using modulation, a carrier waveform can be used that is most compatible with the transmission channel. Typically, these waveforms are high-frequency sinusoids for transmitting signals through space.
A discussion of the reasons data signals are modulated onto carriers is included in Sklar, B., xe2x80x9cDigital Communications: Fundamentals and Applications,xe2x80x9d Prentice Hall, 1988, p. 118, the entire contents of which are incorporated herein by reference. Signals are launched into space via antennas. The design of an antenna is dependent on the wavelength, xcex, of the signal being transmitted. A practical example illustrates one reason why signals are modulated onto high-frequency carrier waves. The wavelength, xcex, of a signal is equal to c/f, where c is the speed of light, or 3xc3x97108 m/s, and f is the frequency of the frequency of the signal being transmitted in Hz. It is well known by those of ordinary skill in the digital communication art that the aperture of an antenna should be at least as large as the wavelength being transmitted (see Sklar, at p. 118). Given this design constraint, it can be shown that a signal with a frequency, f of 3000 Hz has a wavelength, xcex, of c/f, or 105 m, which is approximately 60 miles. Of course, it is not realistic to build an antenna with a 60 mile aperture. However, if that same signal is modulated onto a 30 GHz carrier prior to transmitting it, the antenna can have an aperture of less than xc2xd inch (see Sklar, at p. 118).
Another consideration is the bandwidth required to transmit an ideal square wave. An unmodulated, unshaped ideal square wave requires an infinite amount of bandwidth in the frequency domain. For this reason, it is well known to shape the digital pulses using a filter that will round the edges of the square wave, thereby narrowing the bandwidth of the transmitted signal. Pulse shaping and modulation are discussed in Webb, W., xe2x80x9cThe Complete Wireless Communications Professional: A Guide for Engineers and Managers,xe2x80x9d Artech House Publishers, 1999, pp. 55-64, the entire contents of which is incorporated herein by reference.
When digital information is modulated onto a carrier and transmitted through space, the power spectral density of that signal tends to be concentrated about the frequency of the carrier itself. These signals are normally generated with large antennas and at high power so that the signal is not interfered with by noise. The frequency spectrum is, of course, regulated in the United States by the Federal Communications Commission (FCC). Regulation of the frequency spectrum ensures that there will not be interference within the various allocated frequency ranges. Since all frequency bands contain noise, there is no practical reason to regulate transmissions that are lower than the noise.
With the popularization of the Internet, laptop personal computers, personal digital assistants (PDAs), and cellular telephones, society has become more and more dependent on the availability of information and the ability to share information. With the miniaturization of computing power, many users of information are now demanding mobile access to their information. Using conventional methods, exchanging, and sharing information requires access to network via a telephone connection, or through a direct connection to the network itself. The need for a network limits access to and sharing of information to those that can access the network.
The challenge, then, as presently recognized, is to develop an approach for transmitting and receiving information using, for example, mobile devices such as PDAs, cellular telephones, and laptop personal computers. It would be advantageous if the approach was wireless, eliminating the need for direct connection between the sharing devices. It would be advantageous if the approach were to employ communications techniques that would not fall under the jurisdiction of regulatory agencies, thereby allowing for global use.
An object of the present invention is to provide a method for communicating information using carrierless wireless signals.
The inventors of the present invention have recognized that low power carrierless transmissions can be effectively used to communicate at high data rates without interfering with narrowband or spread spectrum signals, and if the power is kept sufficiently low, the transmissions do not need to be as broadcast devices. Accordingly, another object of the present invention is to encode digital data into multi-phase wavelets that can be transmitted without a carrier at low power and at high data rates over short distances.
In one embodiment, the present invention is implemented as a method for conveying application data with carrierless ultra wideband wireless signals. The application data is encoded into wavelets that are transmitted without modulating them onto a carrier waveform. In another embodiment, the present invention is implemented as a computer data signal that is embodied in a carrierless ultra wideband waveform.
Consistent with the title of this section, the above summary is not intended to be an exhaustive discussion of all the features or embodiments of the present invention. A more complete, although not necessarily exhaustive, description of the features and embodiments of the invention is found in the section entitled xe2x80x9cDESCRIPTION OF THE PREFERRED EMBODIMENTS.xe2x80x9d